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A Boulder mystery: Why did the floor collapse at 4772 Walnut St.?

By Jerd Smith

Business Editor

Posted:
01/28/2017 12:21:19 PM MST

Updated:
01/29/2017 08:34:32 AM MST

The 4772 Walnut building housed the Zayo Group and Sphero, before a partial collapse of the second-story floor Dec. 8, 2016, caused the offices to be evacuated. The building remains vacant. (Cliff Grassmick / Staff Photographer)

More than seven weeks after a second-story floor ripped away from the wall at 4772 Walnut St. in Boulder, an office building where nearly 300 people worked every day, building officials have issued no citations in the incident, nor have they determined what caused the partial collapse.

Dave Thacker, chief building officer for Boulder, said the city is waiting for a forensic engineering report to be completed before determining what if any citations might be issued and what corrective actions might need to be taken. In the meantime, it has issued permits to allow for initial inspections, creation of a "safe passage" for construction workers, the shoring of the building's foundation and the floor's repair.

The 4772 building is one of several in the office park. It was built in 1999 by Boulder-based Wyatt Construction, for a subsidiary of Boulder-based W.W. Reynolds Co., which also developed the office park, according to city records.

Neither Bill Reynolds nor Jeff Wingert, a development manager with the W.W. Reynolds Co., returned requests for comments. W.W. Reynolds no longer owns the building, but continues to manage it. Seattle-based Tierra LLC, which owns the building now, also did not return requests for comment.

Such structural failures in commercial buildings are "unusual," Thacker said. Among the theories under discussion include a weakening of the building's foundation, due to the 2013 floods or a below-ground water leak, but no one has ruled out other causes as well, he said.

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According to a preliminary investigation of the site, a connection tying a massive steel beam to a metal plate embedded in a concrete column sheared off. The beam supported the second floor. What caused the beam connection to fail is unclear.

The building, which now stands vacant, housed 180 employees of Boulder-based Sphero Inc., the company whose toy bot, the BB-8, is forever linked to last year's Star Wars movie, and 100 employees of Boulder's Zayo Group, a telecommunications company. Sphero and Zayo officials declined to comment on the status of the building or the cause of the crash. No employees were injured.

At 10:16 a.m. on Thursday Dec. 8, Zayo Group employees on the first floor heard what they thought was a massive explosion. As they looked up, the power went out and ceiling tiles began falling on desks as dust and smoke filled the room, according to one employee's account.

The massive beam would fall 12 to 18 inches, according to city building and fire officials, before catching on another structural element of the building's frame. If it had fallen to the floor, it would have landed on a vice president's desk, said one employee, who asked not to be identified because she feared it might jeopardize her employment with the Zayo Group.

"It sounded like an explosion," she said. "Everyone was screaming, and someone started yelling 'Get out. We have to get out.' " she said. "It was chaos."

At the same time, upstairs at Sphero, someone activated a fire-alarm, and within five minutes, firefighter Joe Gross, and his engine team, arrived to see dozens of employees milling around outside. Eventually 11 firefighters would be on scene, accompanied by building officials and police.

For several minutes after the initial collapse, one employee was feared missing by her colleagues, until she finally appeared after being trapped in a conference room and having to climb over debris piles to exit the building.

Gross and his colleagues entered the building and began their own inspection, searching first to make sure no one was still trapped inside.

"The second floor had a bow in it. You could see it in the ceiling tiles displaced," Gross aid. "You could also see it on the floor where the concrete separated off the wall. The left side of the (second) floor was separated from the wall in a vertical fashion," Gross said. "There would have been a lot of pressure (as the floor pulled away). To people who were inside at the time of the collapse, it could definitely have sounded like an explosion."

Chief Building Officer Thacker said modern building codes ensure, most of the time, that proper engineering and design are complete well before an initial building permit is ever issued. "If we're not convinced it's safe, we don't issue the permit," Thacker said. "We examine every engineering calculation very thoroughly. Our process is sound."

Firefighter Gross said he had not witnessed such a failure in more than 20 years at the Boulder Fire Department.

"My main concern at the time," Gross said, "is what caused this. I've never seen anything like it."

Eighteen years ago, when 4772 was built, three other buildings of similar design and size were also constructed by Wyatt for W.W. Reynolds: 4730, 4740, and 4750, according to city documents. But Thacker said he has not been asked to inspect them for similar flaws and that such an inspection would be futile until they know what caused the original partial collapse.

More than seven weeks ago, on a cold, sunny December morning, the bottom fell out of the second floor office building at 4772 Walnut St. in Boulder. The cause remains under investigation. (Cliff Grassmick / Staff Photographer)

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